Expansion anchor unit

ABSTRACT

An expansion anchor unit has a first member a leading portion of which is provided with cutter edges for drilling a hole in a support structure, and a trailing portion of which converges in direction away from the leading portion. A second member is provided with a forward end portion matingly engageable with the trailing portion of the first member, and with a rearward end portion engageable by a tool which is operative for jointly rotating both of the members in a sense effecting drilling of a hole in a support structure by the cutter edges. The second member may itself be configurated as an expansion member to be expanded by the first member after the latter has drilled the hole in the support structure, or an additional expansion member may be provided which, after the second member is disengaged from the first member and removed from the hole, is inserted into the hole and forcibly wedged into contact with the first member to be expanded by the same.

United States Patent 1 1 Fischer 1541 EXPANSION ANCHOR UNIT [76]Inventor: Artur Fischer, Altheimer Str. 219,

Tumlingen, Germany [22] Filed: March 27, 1970 [21] Appl. No.: 23,339

[30] Foreign Application Priority Data Sept. 19, 1969 Germany ..P 19 47369.9

[52] US. Cl. ..85/68, 29/432, 175/394 [51] Int. Cl ..F16b 13/06 [58]Field of Search ..85/68, 79, 83, 84, 73, 74,

[56] References Cited 'uNlTED STATES PATENTS FOREIGN PATENTS ORAPPLICATIONS 280,834 l2/I964 Australia ....85/68 1 51 Feb. 13, 1973l,22l,056 7/1966 Germany 85/ 68 Primary Examiner-Marion Parsons, J.

Attorney-Michael S. Striker 57 ABSTRACT An expansion anchor unit has afirst member a leading portion of which is provided with cutter edgesfor drillinga hole in a support structure, and a trailing portion ofwhich converges in direction away from the leading portion. A secondmember is provided with a forward end portion matingly engageable withthe trailing portion of the first member, and with a rearward endportion engageable by a tool which is operative for jointly rotatingboth of the members in a sense effecting drilling of a hole in a supportstructure by the cutter edges. The second member may itself beconfigurated as an expansion member to be expanded by the first memberafter the latter has drilled the hole in the support structure, or anadditional expansion member may be provided which, after the secondmember is disengaged from the first member and removed from the hole, isinserted into the hole and forcibly wedged into contact with the firstmember to be expanded by the same.

9 Claims, 9 Drawing Figures EXPANSION ANCHOR UNIT BACKGROUND OF THEINVENTION The present invention relates generally to expansion anchors,and more particularly to an expansion anchor unit.

Expansion anchors are of course not new per se. They are, in fact,available in a great variety of different types and sizes. One featurewhich most of the known expansion anchors have in common is that a holemust be drilled in a support structure before the expansion anchor canbe connected with the support structure. The drilling of such holesrequires a special drill which, when the hole is completed, is withdrawnto permit insertion of the expansion anchor. However, expansion anchorsmust be used in a great variety of different types of supportstructures, be they soft or hard, wood, plaster board, masonry or thelike. In order to accommodate all of these different possibilities thedrill used for making the hole is usually provided with cutting edges ofhard metal. If, as issometimes the case, such a drill is usedoccasionally for do-it-yourself installation of an expansion anchor,then this arrangement is fully satisfactory. If, on the other hand, thedrill is used frequently for this purpose, as by a craftsman whoinstalls such expansion anchors as a part of his daily routine, thecutting edges will quickly become blunt. While it is true that they canbe sharpened again, this is possible only for a limited number of timesand very quickly the time arrives when the drill must be replaced. This,evidently, is expensive,- just as the repeated sharpening of the cuttingedges of a drill is time-consuming.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to avoid the aforementioned disadvantages.

More particularly it is an object of the present invention to provide animproved expansion anchor unit which, briefly stated, comprises a firstmember having a leading portion provided with cutter edges for drillinga hole in a support structure, and a trailing portion which converges indirection away from the leading portion. A second member is providedwith a forward end portion which is matingly engageable with thetrailing portion of the first portion, and with a rearward end portionwhich is engageable by a tool operative for jointly rotating both thefirst and the second member in a sense effecting drilling of a hole in asupport structure by the cutter edges.

It is clear that the first member of the unit according to the presentinvention thus serves a dual purpose, namely to drill its own hole andsubsequently to act as the expander member of the unit. This is a mostsimple and as time-consuming as inexpensive method of mounting anexpansion anchor unit in a support structure, and it requires no toolsother than those previously needed, namely a power drill. Moreover,every time an expansion anchor unit is to be mounted in asupportstructure, a new set of cutting edges is available, so that. noloss of cutting efficiency due to blunting of the edges from theprevious formation of an expansion anchor hole is experienced. It is nolonger necessary to sharpen blunted cutting edges, and the lost time andincreased expense involved previously in sharpening such cutting edgesand eventually discarding the drill entirely have been eliminatedaccording to the present invention.

Moreover, the material and the hardness of the first member providedwith the cutter edges can be selected in accordance with the fact thatthe cutter edges need withstand only a single drilling application,namely when the hole is drilled for the expansion anchor unit of whichthe first member having the cutting edges is a part. Thus, material canbe used which is considerably less expensive than heretofore wasnecessary for making separate drills.

In addition, the first member is much more readily connectable with anddisconnectable from the second member, and vice versa, than thefrequently necessary removal and subsequent re-insertion of aconventional drill in the chuck of a power drilling machine.

The second member may itself serve exclusively the purpose of engagingthe first member while the latter is used to drill a hole in the supportstructure. Subsequently, the second member may be removed and a thirdmember, also constituting a part of a novel expansion anchor unitaccording to the present invention, may be inserted into the bore holein such a manner and to such an extent that is is expanded into tightengagement with the wall surrounding the hole by the first member whichat the completion of the drilling step has remained in the bore hole.The formation of the bore hole and the mounting of the expansion anchorunit therein is extremely simple when utilizing a unit according to thepresent invention, and it is fast as well as in expensive. The thirdmember is essentially rod or bolt-shaped and optimum holding conditionsin the bore hole are obtained if the diameter of the third membercorresponds to the diameter of the bore hole formed by the first member.

The latter may be provided, incidentally, on its oppositelylongitudinally extending surfaces with one or more projecting ribs orprojections which are elongated substantially in longitudinal directionof the first member and engage in corresponding mating recesses providedon the second member or the third member, or on both. Such projectioncan be formed in simple manner by cold deformation when the first memberis produced, and they may converge gradually in the direction towardsthe leading portion and the cutter edges of the first member, which isto say that they diverge in the opposite direction and thus act as awedge which facilitates radial expansion of the expansion memberassociated with and forming a part of the novel unit. Their majorpurpose, however, is to provide proper engagement with either the secondmember or the third member, to prevent displacement of the first memberwith reference to either one of the others. Of course, these projectionsmay have other configurations, and may be located at different points ofthe first member as long as mating recesses are correspondingly providedon the second and/or third member.

The second and/or third member may be provided with two or morehelically convoluted grooves in its outer circumferential surface, thepurpose being to I allow escape of comminuted material of the support atleast substantial axial parallelism with the axis of the second and/orthird member, and the projections of the first member will be lodged inthese terminal sections. So constructed, a-particularly simple and easyconnection of the first member with the second and/or third member isachieved, and correspondingly an. equally simple and easy disconnectionis obtainable. On the other hand, the projections abut against thelateral surfaces bounding the terminal sections of the grooves and thusrotation of the first with reference to the second and/or third membersis prevented during drilling. Such abutment further serves theadditional purpose of preventing deformation or breaking of theprojections during drilling.

it is advantageous if the first member is in form of a rather flatelongated member with the projections being located on the two oppositelateral surfacesof the same. Two or more such projections may beprovided, and if there are two of them then they may be offset withreference to one another. The second and/or third member may be providedwith a longitudinal slot, corresponding to the thickness of the firstmember-that is the dimension between the aforementioned two surfaces ofthe same-and in which the first member is partially receivable with itsleading portion formed with the cutter edges extending forwardly beyondthe slot. The outer circumferential surface of the second member may beprovided with recesses in diametrally opposite edges bounding the slotand in these recesses the projections of the first member may be lodgedwhen the first member is temporarily connected with the second memberfor drilling purposes. A first member-so configurated is particularlyeasy to manufacture, and the projections may be formed simply by astamping process as the first member is being manufactured. Similarly,the slot may be readily provided by milling or in other suitable mannerin the second member, and the recesses are then subsequently formed alsoin suitable manner, for instance bymilling. The opposite location of theprojections,

and the diametrally opposite location of the recesses, assures thatlateral sliding of the first member out of the slot of the second memberis prevented so that the first member will always be centered withreference to the second member, a consideration which is importantduring'drilling.

The projections may be outwardly convexly curved, to facilitate and easethe expansion when the second member, or the third member, as the casemay be, is driven into the bore hole to the extent necessary to providesuch expansion. When such convex configuration is chosen, then therewill only be a line contact between the projections and the engagingsurface portions of the second or third member, so that very littlefriction is opposed tothe forcible insertion of the second or third'member' into the bore hole, making it possible for the second or thirdmember to be readily driven far into the bore hole withthe first memberentering far into the slot of the second or third member and therebyobtaining an excellent engagement of the expansion anchor unit in theexpansion anchor hole, having a high resistance to forces tending todraw the unit out of the hole.

The projections may gradually merge out of the respective surfaces ofthe first member, so as to diverge in direction towards the cutter edgesthereof. However, it is possible to have the projections merge fromtheir widest or most divergent portion gradually tapering in thedirection towards both the leading and the trailing portion of the firstmember. This latter construction makes it possible to effect entry ofthe first member into the longitudinal slot of the second or thirdmember.

in either direction, a consideration which is particularly of importanceif the second member is not only an engagement for the first memberduring drilling with the latter, but also constitutes the expansionmember of the anchor unit. In this case the first member will abutagainst an abutment portion in the slot of the expansion member so thatthe latter is not already expanded during the drilling period.Subsequently, the expansion member is withdrawn partially or completelyfrom the bore hole, at least to such an extent as to disconnect it fromthe first member, turned in circumferential direction until itslongitudinal slot becomes aligned with the trailing portion of the firstmember, and then forcibly inserted into engagement with the first memberin a sense effecting the necessary expansion.

If the first member is of relatively flat configuration, and theprojections are located centrally on opposite surfaces thereof, thisaffords the possibility to form the second or third member with twoslots which cross one another so that at least the forward end portionof the second or third member is subdivided into four sections.Insertion of the second or third member into the bore hole in a sensecausing expansion by the first member then results in radial expansionof all four sections in four different directions, thus assuring astrong uniform expansion in all directions and a good anchoring of theunit. Moreover, the initial drilling characteristics afforded by a flatcutting edge are of course highly advantageous and can be provided bymaking the first member of flat configuration.

Of course, the most simple form of the novel expansion anchor unit isfor the second member to be not only the engaging member which engageswith its forward end portion the first member and with its rearward endportion a drilling tool, such as a power drill, but also to actsubsequently to drilling as the expansion member itself which becomesexpanded in and anchored in the bore hole in the support structure. Thisis not only the most inexpensive type of expansion.

anchor unit according to the present invention, but also requires theleast amount of work for its installation. It goes without saying thatwith such a construction stocking problems are also greatly reduced.

A very simple manner of making the second or third member of the novelexpansion anchor unit is to take a length of rod of polygonalcross-sectional configuration and to twist it about its longitudinalaxis, providing it at its forward end portion with engaging means forengaging the first member, and forming a longitudinal slot permittingsubsequent radial expansion. The slot may be increased stepwise forfacilitating such expansion.

This method of construction provides in a most simple manner the helicalgrooves in the outer circumferential surface of the second member whichare desirable for escape of comminuted material of the supportstructure. The stepwise increase of the longitudinal slot has theadditional advantage that the first step may serve as an abutment forthe first member while the same is used to drill a bore hole in asupport structure, so that premature expansion of the second member bythe first member is avoided. At the same time this guarantees that theleading portion of the first member provided with the cutter edges willalways project forwardly of the forward end portion of the secondmember, always assuming of course that the first step of the slot islocated at such a spacing rearwardly from the forward end of the secondmember that this relationship is obtained.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view showingone embodiment of a first member for an expansion anchor unit accordingto the present invention;

FIG. 2 is a view similar to FIG. 1 but illustrating a further embodimentof the first member;

FIG. 3 is a perspective view showing a second member for use with one ofthe members of FIGS. 1 and 2;

FIG. 4 is a perspective view showing a third member which, together withthe member of FIG. 3 and one of the members of FIGS. 1 and 2,constitutes an expansion anchor unit according to the present invention;

FIG. 5 is a view analogous to FIG. 4 but showing a member which bothserves to connect one of the members of FIGS. 1 and 2 with thenon-illustrated power drill, and which subsequently serves as theexpansion member of a two-member anchor unit;

FIG. 6 is a perspective view similar to FIG. 1 but illustrating yet anadditional embodiment of the first member;

FIG. 7 is an end view of a member similar to that of FIG. 6 but providedwith different projections;

FIG. 8 is a cross-sectional view illustrating another embodiment of amember analogous to that of FIG. 6 but provided with differentprojections and inserted in an expansion member; and

FIG. 9 is a perspective view of a second or third member for anexpansion anchor unit according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing indetail and firstly the embodiment illustrated in FIG. 1, it will be seenthat what I have shown in this Figure is a first member for a two-partor three-part expansion anchor unit according to the present invention.The member 1 in FIG. 1 is the expander and drilling member of the unitand is provided with a trailing portion 2 serving subsequently forexpansion of the expansion member of the unit, and with a leadingportion 3 which is formed with conventional cutting edges 4. Thetrailing portion 2 is provided with a U-shaped cutout 5 extendingtowards but short of the leading portion 3 and being bounded at oppositesides by the arms or legs 6. These, it should be noted, conically orfrustoconically taper in the direction away from the leading portion 3of the member 1. At opposite longitudinally extending surfaces 8 (onevisible) the member 1 is provided with respective substantiallycentrally located projections 9 which diverge outwardly of therespective surface 8 in the direction towards the leading portion 3 andserve to further facilitate expanding or spreading of an expansionmember associated with the member 1 as part of an expansion anchor unitaccording to the present invention.

' The bottom wall 7 of the cutout 5 constitutes an abutment.

The embodiment illustrated in FIG. 2 differs from that in FIG. 1 in thatthe member 10 which replaces the member 1 of FIG. 1, has its leadingportion 11-corresponding to the portion 3 of the member 1 in FIG. lmadeof a thinner, flatter configuration than the portion 3 of the member 1.In other respects the member 10 corresponds to the member 1.

The member 12 identified and illustrated in FIG. 3 is not an expansionmember, but only constitutes a connecting member connecting the member 1with a power drill or the like used to rotate the member 1 'so that thecutting edges 4 thereof will drill a hole in the non-illustrated supportstructure. A unit utilizing the member 12 must therefore have anadditional member which constitutes the expansion member of the unit andis identified with reference numeral 20 in FIG. 4, which will bediscussed presently. The member 12 in FIG. 3 is provided in its outercircumferential surface with at least two helically convoluted grooves13 through which comminuted material of the support structure can escapefrom the bore hole, thus facilitating the drilling operation. At itsforward end portion 14 the member 12 is provided with a centrallylocated impression 15 whose length and width-but not depth-correspondsto the respectively corresponding dimensions of the member 1 of FIG. 1or the member 10 of FIG. 2. The depth of the depression 15 is such thatwhen the member 1 or the member 10 is partially received therein, thebottom face 7 bounding the respective cutout 5 will abut against thebottom face 16 bounding the depression 15, with the respective leadingportion 3 or II and the cutting edges provided thereon, extendingforwardly from the forward end portion 14. According to the presentinvention the terminal sections of the grooves 13 extend in at leastsubstantially parallelism with the longitudinal axis of the member 12,as shown in FIG. 3, and the arms or legs 6 of the members 1 or 10 arereceived in these terminal sections at diametrally opposite sides of themember 12 when the members 1 or 10 are connected with the member 12,with the arms or legs 6 abutting against the side faces 17 bounding thegrooves, or rather the terminal sections of the grooves 13, to preventrelative rotation between the members 12 and l or 10 respectively. Theside faces 18 bounding the recess 15 serve the same purpose. Therearward portion 19 of the member 12 is configurated so it can beengaged readily by a tool, such as a power drill, which is used torotate the members 12 and l or 10 in unison, so that the members 1 or 10will form their own bore holes in a support structure.

As mentioned before, an expansion anchor unit according to the presentinvention which utilizes either the member 1 or the member 10 of FIGS. 1and 2 in conjunction with the member 12 of FIG. 3 also requires anexpansion member which is identified with reference numeral 20 in FIG.4. It will be seen that it is provided with a conically tapering kerf 22in its leading end face 21, with this kerf merging into an axiallyextending slot 23 which extends through the member 20 almost half waytowards the trailing end face 26 thereof. The slot 23 subdivides theforward portion of the member 20 into two sections 24 which are spreadapart in radial direction when the member 20 is inserted into aboresubsequent to withdrawal of the member l2-and forcibly driven intothe bore hole until the trailing portion 2 of the member 1 (or thetrailing portion 2 of the member 11) first enters the kerf 22 andsubsequently the slot 23, thus effecting radial spreading of thesections 24. A plurality of sawtooth-profiled circumferential ridges 25is provided at least on the forward portion of the member 20, to affordtighter engagement of the sections 24 with the material of the supportstructure surrounding the bore hole. The trailing portion of the member20 is provided with an outer screw thread 27 which extends oversubstantially one third of the length of the member 20, the intentionbeing that the portion provided with the screw thread 27 will extendoutwardly from the bore hole after the sections 24 have been expanded tothe maximum extent, so that an article to be secured to a supportstructure by means of the novel expansion anchor unit can be mounted onthis outwardly extending portion, with a nut or the like being used tomesh with the screw threads 27 and secure such article in place. It goeswithout saying, of course, that the rear portion of the member 20 couldalso be hollow and the screw threads provided internally.

Coming to the embodiment in FIG. 5 it will be seen that the member 28illustrated therein replaces the members 12 and 20 of FIGS. 3 and 4. Themember 28 thus can be used with the members 1 or 10, respectively, andconstitutes with either one of the two a twomember expansion anchorunit, rather than the threemember expansion anchor unit previouslydescribed. The member 28 is provided not only with the slot 23- and alsowith the projections 25 corresponding to those of the member 20 in FIG.4-but with an additional depression or recess corresponding to the oneidentified with reference numeral 15 in FIG. 3, and extending in a planetransverse to the plane of the slot 23. This recess or depression isidentified with reference numeral 29. Extending rearwardly from therecess or depression 29 in axial direction of the member 28 and locatedat diametrally opposite sides of the member 28 are grooves 30 providedin the outer circumferential surface of the member 28. Thus, the members1 or can be connected with the member 28 in the same manner as they canbe connected with the member 12 in FIG. 3, and their arms or legs 6 willbecome lodged in the grooves 30. The latter, incidentally, can be formedby milling or in other suitable manner.

FIG. 6 shows that the member lacorresponding to the members 1 and 10 ofFIGS. 1 and 2, respectivelycan be provided on its trailing portion 2awith elongated ridges 9a which extend substantially lengthwise 5 of themember 1a, diverging outwardly from the respective surfaces in thedirection towards the leading portion 3 of the member 1a. They each have(one pro jection 9a is shown) a longitudinally extending abutment edge40.

FIG. 7 shows an embodiment which corresponds essentially to that of FIG.6, except that the projections 9a of FIG. 6 are replaced by projections90, differing from the projections 9a only in that they are convexlycurved in direction outwardly away from the respective surfaces on whichthey are provided.

The embodiment of FIG. 8 shows, in section and inserted in a member 19awhich is illustrated in FIG. 9, a further possible embodiment of themember 1a shown in FIG. 6. It is modified in so far as in FIG. 8 themember la'--corresponding to the member 1a of FIG. 6-is provided withlongitudinally extending projections 9b which are produced bydeformation pressure,

whereas those of the embodiment in FIG. 7 may for in stance be producedby cold forming of the material.

The member 19a shown in perspective in FIG. 9 in fragmentary form andshown in section in FIG. 8 is provided with a longitudinal slot 23corresponding to the similar slots in the preceding Figures. The membershown in FIG. 7, or the member 10 shown in FIG. 8, can be inserted intothis slot 23 for drilling purposes, and the projections 9a or 9b ofFIGS. 7 and 8 will become lodged in the grooves 41 which are formed, asclearly shown, in the outer circumferential surface of the member 19aalong diametrally opposite lateral edges of the slot 23. The projections9a or 9b abut against the surfaces 42 bonding one side of the grooves41, as evident for instance from FIG. 8. Of course, the projections 9aor 9b diverge in the same sense and direction as the projections 9a inFIG. 6. Thus, and because of their outwardly convex configuration, thereis only line contact between them and the surfaces bounding a slot in anexpansion member of the anchor unit, and this facilitates forcibleinsertion of the expansion member into the bore hole.

It will be appreciated that member 19a corresponds-as illustrated-to themember 12 of FIG. 3, that is an expansion anchor unit utilizing themember 19a and for instance the member la of FIG. 8, will additionallyhave a third member corresponding for instance to the member 20 of FIG.4. However, it would also be possible to modify the member 19a in such amanner that it could be used in the same manner as the member 28 of FIG.5, thus combining the functions of the members 12 and 20 of FIGS. 3 and4, respectively.

Of course, various different materials including, but not limited to,metallic material are suitable for the various members of the expansionanchor units illustrated herein.

The invention also relates to a highly advantageous method of mountingan expansion anchor unit according to the present invention in a supportstructure. 65 Specifically, the member 12 is releasably engaged with oneof the members 1 or 10, or the member 19a is releasably engaged with forinstance the member shown in FIG. 7 or the member la shown in FIG. 8,

and the members 18 or 19a are then in turned engaged with the chuck of apower drill or the like, and rotated so that the cutting edges 4 of themembers 1, 10, la or the like will form a bore hole in a supportstructure against which the cutting edges 4 are placed. Thereupon, themember 12 or 19a is withdrawn from the bore hole, leaving the associatedmember (for instance the member 1) behind in the bore hole. Now, anexpansion member, such as the member 20 of FIG. 4, is inserted into thebore hole and forcibly driven into the same until the trailingportionfor instance the trailing portion 2 of the member 1-enters intothe slot 23 and expands the sections 24 into tight engagement with thematerial surrounding the bore hole. Of course, other expansion anchorunits according to the present invention may be utilized in differentmanner, for instance the unit which has as one of its two constituentcomponents the member 28 of FIG. 5.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in anexpansion anchor unit, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the specific or generic aspects of this inventionand, therefore, such adaptation should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. An expansion anchor system comprising a first member of substantiallyflat configuration and having a leading portion provided with cutteredges for drilling a hole in a support structure, and a trailing portionconverging in direction away from said leading portion and having afirst engaging portion extending towards said leading portion; a secondmember provided with a forward end portion having a second engagingportion extending rearwardly and being matingly but releasablyengageable with said first engaging portion of said trailing portion ofsaid first member, and with a rearward end portion engageable by a tooloperative for jointly rotating both of said members in a sense effectingdrilling of a hole in a support structure by said cutter edges; a thirdmember having a front portion and a screw-threaded rear portion, saidthird member being provided with at least one third engaging portion inform of a slot dimensioned for entry of said first member and extendingfrom said front portion towards said rear portion so as to subdivide atleast the former in two parallel sections which spread apart in radiallyoutward direction in response to forcible axial insertion of said thirdmember into the drilled hole subsequently to disengagement of saidsecond member from said first member and withdrawal of said secondmember, the

ent of said first member into said third member resu ting in radialexpansion of said front portion into wedging engagement with the wallbounding said hole.

2. A system as defined. in claim 1, said first member having twoopposite sides, a pair of projections each being provided on one of saidsides and offset with reference to the other projection; wherein thesecond member has an outer circumferential surface and is provided witha rearwardly extending slot in said forward end portion and a pair ofelongated recesses extending rearwardly in said forward end portionalong respective diametrally opposite edges of said slot, for receivingthe respective projections therein when said first member is in partlocated in said slot; and wherein said third member is also providedwith a pair of elongated recesses in its outer circumference extendingrearwardly in said front portion along respective diametrally oppositeedges of said slot in said third member.

3. A system as defined in claim 1, said first member having twotransversely spaced surfaces extending between opposite ends of saidleading and trailing portions; further comprising at least a pair ofprojections each provided on one of said surfaces and elongatedsubstantially in direction between said opposite ends;

' and mating recesses provided in said forward end portion of saidsecond member and said front portion of said third member and beingpositioned to receive the respective projections for preventingdisplacement of the respectively engaged members with reference to oneanother.

4. A system as defined in claim 3, said second member having an outercircumferential surface; and further comprising at least two helicallyconvoluted grooves provided in said outer surface extending between theaxial ends of said forward and rearward end portions and each having inthe region of said forward end portion a groove section which extends inat least substantial parallelism with the longitudinal axis of saidsecond member and constitutes one of said mating recesses.

5. A system as defined in claim 3, said projections being convexlycurved in direction outwardly from the respective surface.

6. A system as defined in claim 1, said second member being of polygonalcross-section and helically twisted about its longitudinal axis.

7. A system as defined in claim 6, wherein the crosssection of saidthird member decreases stepwise in direction from said rear portiontowards said front portion.

8. A system as defined in claim 1; further comprising a plurality ofridges provided on an outer circumferential surface of at least saidfront portion and encircling the latter.

9. A system as defined in claim 8, wherein said ridges are ofsawtooth-shaped profile.

m 1s in at s

1. An expansion anchor system comprising a first member of substantiallyflat configuration and having a leading portion provided with cutteredges for drilling a hole in a support structure, and a trailing portionconverging in direction away from said leading portion and having afirst engaging portion extending towards said leading portion; a secondmember provided with a forward end portion having a second engagingportion extending rearwardly and being matingly but releasablyengageable with said first engaging portion of said trailing portion ofsaid first member, and with a rearward end portion engageable by a tooloperative for jointly rotating both of said members in a sense effectingdrilling of a hole in a support structure by said cutter edges; a thirdmember having a front portion and a screwthreaded rear portion, saidthird member being provided with at least one third engaging portion inform of a slot dimensioned for entry of said first member and extendingfrom said front portion towards said rear portion so as to subdivide atleast the former in two parallel sections which spread apart in radiallyoutward direction in response to forcible axial insertion of said thirdmember into the drilled hole subsequently to disengagement of saidsecond member from said first member and withdrawal of said secondmember, the entry of said first member iNto said third member resultingin radial expansion of said front portion into wedging engagement withthe wall bounding said hole.
 1. An expansion anchor system comprising afirst member of substantially flat configuration and having a leadingportion provided with cutter edges for drilling a hole in a supportstructure, and a trailing portion converging in direction away from saidleading portion and having a first engaging portion extending towardssaid leading portion; a second member provided with a forward endportion having a second engaging portion extending rearwardly and beingmatingly but releasably engageable with said first engaging portion ofsaid trailing portion of said first member, and with a rearward endportion engageable by a tool operative for jointly rotating both of saidmembers in a sense effecting drilling of a hole in a support structureby said cutter edges; a third member having a front portion and ascrew-threaded rear portion, said third member being provided with atleast one third engaging portion in form of a slot dimensioned for entryof said first member and extending from said front portion towards saidrear portion so as to subdivide at least the former in two parallelsections which spread apart in radially outward direction in response toforcible axial insertion of said third member into the drilled holesubsequently to disengagement of said second member from said firstmember and withdrawal of said second member, the entry of said firstmember iNto said third member resulting in radial expansion of saidfront portion into wedging engagement with the wall bounding said hole.2. A system as defined in claim 1, said first member having two oppositesides, a pair of projections each being provided on one of said sidesand offset with reference to the other projection; wherein the secondmember has an outer circumferential surface and is provided with arearwardly extending slot in said forward end portion and a pair ofelongated recesses extending rearwardly in said forward end portionalong respective diametrally opposite edges of said slot, for receivingthe respective projections therein when said first member is in partlocated in said slot; and wherein said third member is also providedwith a pair of elongated recesses in its outer circumference extendingrearwardly in said front portion along respective diametrally oppositeedges of said slot in said third member.
 3. A system as defined in claim1, said first member having two transversely spaced surfaces extendingbetween opposite ends of said leading and trailing portions; furthercomprising at least a pair of projections each provided on one of saidsurfaces and elongated substantially in direction between said oppositeends; and mating recesses provided in said forward end portion of saidsecond member and said front portion of said third member and beingpositioned to receive the respective projections for preventingdisplacement of the respectively engaged members with reference to oneanother.
 4. A system as defined in claim 3, said second member having anouter circumferential surface; and further comprising at least twohelically convoluted grooves provided in said outer surface extendingbetween the axial ends of said forward and rearward end portions andeach having in the region of said forward end portion a groove sectionwhich extends in at least substantial parallelism with the longitudinalaxis of said second member and constitutes one of said mating recesses.5. A system as defined in claim 3, said projections being convexlycurved in direction outwardly from the respective surface.
 6. A systemas defined in claim 1, said second member being of polygonalcross-section and helically twisted about its longitudinal axis.
 7. Asystem as defined in claim 6, wherein the cross-section of said thirdmember decreases stepwise in direction from said rear portion towardssaid front portion.
 8. A system as defined in claim 1; furthercomprising a plurality of ridges provided on an outer circumferentialsurface of at least said front portion and encircling the latter.